Method and apparatus for redirecting data traffic based on external switch port status

ABSTRACT

Method for redirecting outbound VLAN traffic away from an inactive external port of a switch. A first switch monitors the active or inactive status of a designated external port. A host computer periodically queries the first switch requesting the status of the designated external port. The first switch replies to the query indicating the current status of the designated external port. If the external port is inactive, the host computer redirects data traffic away from the inactive designated external port to an alternate external port without deactivating the designated internal port. Preferably, the designated internal port continues to be used for secure internal LAN communications, such as between a host computer and a management entity. When the designated external port is again active, data traffic is returned to the designated external port.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods and systems for managingtraffic to and from a host computer, such as a server blade, in responseto the active or inactive status of an external switch port.

2. Background of the Related Art

A typical computer system will include a network interface card thatallows the computer system to communicate with a network. In a serverblade chassis, multiple server blade computers each have at least onepair of network interface cards that are connected to an internalchassis switching system. This chassis switching system communicateswith the network through one or more external switching systems.However, if any of the communication links fail or become unavailable,communications from the server blade(s) using that link can become lost.

A virtual local area network (VLAN) is a group of hosts with a commonset of requirements that communicate as if they were attached to thebroadcast domain regardless of their physical location. A VLAN has thesame attributes as a physical local area network (LAN), but it allowsfor end stations to be grouped together even if they are not located onthe same network switch. Accordingly, network reconfiguration can bedone through software instead of physically relocating devices.

A VLAN trunk is typically used to carry communications for multiplelogical networks over a common physical link. An intermediate Layer 2switch or bridge device may forward a subset or all VLANs associatedwith an internal VLAN trunk to an external link. Loss of the externallink may thus impact a subset or all of the VLAN traffic(communications) associated with the internal trunk link. It istherefore important to quickly detect the loss of the link and takesteps to re-establish communication with the network.

Accordingly, a host computer station may include a firmware agent thatperiodically issues a TCP/IP ping or an address resolution protocol(ARP) request to a remote target computer station. An activecommunication will result in a return response. The absence of a returnresponse is an indication to the firmware agent that the path betweenthe host and the remote station is inactive. The firmware agent of thehost will then initiate recovery action(s) to redirect outbound trafficto another physical path and continue to test the inactive link todetermine when the path to the remote station has been reactivated.Although this method is typically used to detect loss of a physicalpath, it is also applicable to loss of a logical path, such as throughan intermediate router or gateway. Loss of the path is implied byabsence of a response from the remote station.

Patent Publications US 2006/0206602 and US 2006/0203715 describe amethod and system that redirects traffic from a server blade todifferent access switches that each provide data communication with anetwork. The server blade has a primary interface associated with afirst access switch and secondary interface associated with a secondaccess switch. Each access switch has external ports directed toward anetwork, and corresponding internal ports directed toward the serverblades. In the event that a first access switch loses a data signal orconnection at one or more of its external ports, the correspondinginternal port(s) is (are) automatically disabled. The disabling of theinternal port causes the primary interface in the server blade tofailover to the secondary interface that is coupled to the second accessswitch.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the present invention provides a method forredirecting outbound VLAN traffic away from an inactive external port ofa switch within a blade server chassis. The method comprises a firstswitch monitoring the status of a designated external port, wherein thestatus of the designated external port is selected from the groupconsisting of active and inactive. A host computer within a blade serverchassis periodically sends a query to the first switch to request thestatus of the designated external port, wherein the host computer has afirst connection to a designated internal port that is mapped to thedesignated external port of the first switch and a second connection toan alternate internal port that is mapped to an alternate external port.In response to receiving the query, the first switch provides a replycommunication to the host computer, wherein the reply communicationincludes the status of the designated external port. Then, in responseto receiving the reply communication from the switch indicating that thestatus of the external port is inactive, the host computer redirectsoutbound VLAN traffic away from the inactive designated external portthrough the alternate internal port to the alternate external portwithout deactivating the designated internal port.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary server blade system chassisincluding multiple server blades and two intermediate Layer 2 devices.

FIG. 2 is a port status table that exemplifies data that is maintainedby an intermediate Layer 2 device or the chassis management subsystem.

FIG. 3 is a flowchart of a method of managing data traffic between ahost computer and a network.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention provides a method forredirecting outbound VLAN traffic away from an inactive external port ofa switch within a blade server chassis. The method comprises a firstswitch monitoring the status of a designated external port, wherein thestatus of the designated external port is selected from the groupconsisting of active and inactive. A host computer within a blade serverchassis periodically sends a query to the first switch to request thestatus of the designated external port, wherein the host computer has afirst connection to a designated internal port that is mapped to thedesignated external port of the first switch and a second connection toan alternate internal port that is mapped to an alternate external port.In response to receiving the query, the first switch provides a replycommunication to the host computer, wherein the reply communicationincludes the status of the designated external port. Then, in responseto receiving the reply communication from the switch indicating that thestatus of the external port is inactive, the host computer redirectsoutbound VLAN traffic away from the inactive designated external portthrough the alternate internal port to the alternate external portwithout deactivating the designated internal port.

Where the switch, or other intermediate Layer 2 device, provides aone-to-one mapping of internal ports to external ports, such as commonto so-called “pass-through devices” within a blade server chassis, thestatus of the designated external port is sent to the host computer viathe corresponding designated internal port. The host device can use thedesignated external port status information to enable redirecting ofselected VLAN traffic to an alternate external port, such as analternate VLAN trunk, when the designated external port is inactive.Beneficially, the designated internal port to the switch remainsoperable to traffic not affected by loss of the designated externalport.

The port status information is maintained by an intermediate Layer 2device, such as a switch, or an intermediate proxy agent, which may bepart of a management system. The port status information includes theinstantaneous status of each of the external ports of the switch andoptionally includes the identification of a corresponding internal port(although this later identification may be fixed in a pass-throughdevice). A list of VLAN identifications associated with a particularinternal or external port is also maintained, either by the switch, theintermediate proxy agent, or the host computer.

The host computer periodically queries the switch or intermediate proxyagent, whichever is maintaining the port status information to requestthe status of the designated external port. The device maintaining theport status information responds appropriately based upon theinstantaneous port status to indicate the status of the associatedexternal link(s) to the host computer. The host computer responds to aninactive designated external port by redirecting traffic that isassociated with that port. All traffic or VLANs from the host computerthat does not rely upon the inactive external port can continue toutilize the designated internal port, which remains active.

The host computer continues to monitor the status of the external link,via the same procedure of queries and responses, to determine when thedesignated external port has been reactivated. Responses provided by thedevice maintaining the port status information may be either explicit orimplicit. For example, an implicit response may include a switch notproviding a response to an ARP request or PING. An explicit response maybe in the form of a message or indication that a specific port has infact become inactive or reactivated.

The foregoing methods offer several advantages over existing methods ofredirecting traffic away from an inactive external port of a switch. Thenetwork message exchange between the host and intermediate device isconstrained and does not involve an additional remote device or networklinks. This method is particularly applicable to blade server chassissystems, but is applicable to conventional rack systems. Furthermore,the present methods can utilize existing host computer methods with theswitch implementation customized to map specific internal and externalports.

In an additional embodiment, the switch maintains an ordered list of alldesignated external ports and the internal port corresponding to eachexternal port. The status of each external port of the switch ismaintained in a record as an indicator of the link's status (e.g.,active, inactive, etc.). In one embodiment, a firmware agent within thehost station periodically issues a query packet (such as a TCP/IP ARPRequest or PING) to a unique IP address within the switch. The sourceMAC address or other unique content of the query packet can be used bythe switch to determine the physical identification of the internalport, thus forming an index into the port status table. Other meansspecific to the switch may be used to form the index as well.

In this embodiment, an agent within the switch will issue a positiveresponse to the PING if the corresponding external port is active (i.e.,the external port mapped to the internal port from which the queryoriginated). Otherwise, the switch will issue a negative response (or noresponse at all) if the corresponding external port is inactive. Thehost computer, optionally through use of a firmware agent, will take theappropriate action if a negative response is received. For example, thehost firmware agent may take action to redirect all VLAN trafficassociated with an inactive external port to another path (e.g.,separate physical port or network interface card (NIC)). The hostcomputer will continue to maintain an active link with the internal portof the switch and will periodically query to determine when the externalport has been reactivated. Likewise, any VLAN traffic that may have beenassociated with other external or internal ports of the switch willcontinue to flow from the host over the internal link. This is unlikethe methods disclosed in US 2006/0206602 entitled Network Switch LinkFailover in a Redundant Switch Configuration or in US 2006/0203715entitled Method for Redirection of Virtual LAN Network Traffic. In bothof these publications, the designated internal port is deactivated bythe switch and all VLANs associated with the designated internal portmust be redirected to an alternate internal link.

In another embodiment, a management entity (e.g., intermediate proxydevice) separate from the Layer 2 device maintains the port statusinformation that is acquired from the Layer 2 device and responds onbehalf of the Layer 2 device to query packets issued by attached hostagents. Such operation to separate the management entity from the Layer2 physical device may be transparent to the host computer or host agent.In the context of a server blade chassis, the intermediate proxy devicemay be the chassis management module.

FIG. 1 is a block diagram of an exemplary server blade system chassis 10including multiple server blades 12A-C, two intermediate Layer 2 devices20A-B, and an intermediate proxy device, such as chassis managementsubsystem 40. Each of the server blades or host devices 12A-C (onlythree shown) have a pair of network interface cards (NIC) that enableinbound and outbound communications, for example using an Ethernetprotocol. For example, the server blade 12A has a first NIC 14A that iscoupled to a first internal port 22A of the “designated” intermediateLayer 2 device 20A and a second NIC 14B that is coupled to a firstinternal port 24A of the “alternate” intermediate Layer 2 device 20B.The term “designated” is used here to indicate the device that bladeserver 12A is instructed to use as its primary path for communicationwith an external network 45. The server blade 12A will utilize thedesignated device 20A unless the path becomes inactive. Similarly, theserver blades 12B, 12C each have a first NIC 16A, 18A, respectively,that is coupled to an internal port 22B, 22C, respectively, of the“designated” intermediate Layer 2 device 20A and a second NIC 16B, 18B,respectively, that is coupled to an internal port 24B, 24C,respectively, of the “alternate” intermediate Layer 2 device 20B.Accordingly, each blade server or host computer can communication witheither or both of the intermediate Layer 2 devices 20A, 20B. It ispossible for a host computer to use both NICs at the same time. The hostcomputer is preferably responsible for ‘balancing’ the amount of trafficpassing through these two ports.

The intermediate Layer 2 devices 20A, 20B are shown as “pass-through”devices in which each of the internal ports is mapped to exactly oneexternal port. For example, the designated intermediate Layer 2 device20A shows its internal ports 22A-C mapped to corresponding or associatedexternal ports 26A-C. Accordingly, a collection of informationidentifying the internal ports and which external port is mapped to eachinternal port may be referred to as a “port association record.” A portassociation record for the system in FIG. 1 would also indicate that theinternal ports 24A-C of the alternate intermediate Layer 2 device 20Bare associated with the external ports 28A-C, respectively. Theassociations within the devices 20A, 20B are generally notuser-configurable, but are set by the manufacturer.

Each internal link is coupled to a host computer and the associatedexternal link is coupled to a network. The host computer sends outboundtraffic from its network interface card to the internal link of theswitch, and then the switch forwards the outbound traffic through theexternal link to the network. Conversely, inbound traffic from thenetwork, presumably originating from a remote computer, is received atthe external link, and then the switch forwards the inbound trafficthrough the internal link to the host computer.

However, a preferred server blade chassis also includes a chassismanagement subsystem or module 40 that is coupled to both the designatedand alternate intermediate Layer 2 devices 20A, 20B over separate lines32, 34, respectively, in order to communicate with the host computersover one or more internal secure VLANs. These communications (internalVLAN traffic) do not rely upon the external links 26A-C, 28A-C and arenot affected by loss of the external link(s). An important aspect of thepresent invention is that this internal traffic can be maintained overthe designated internal ports 22A-C even when the associated externalports 26A-C become inactive, because the internal ports remain active.However, in certain embodiments (as shown) internal managementcommunications between the chassis management subsystem 40 and one ormore of the host computers 12A-C may be provided over a direct internalcommunication path 36, 37 or 38, respectively.

A further discussion about the operation of the invention is facilitatedthrough a specific example. According to details provided in FIG. 1,selected VLANs (e.g., 400, 410) provide access between the server blades12A-C and the chassis management subsystem 40 via the designatedintermediate Layer 2 device 20A. Conversely, certain VLANs (e.g., 100,200) are associated with specific external ports 26A, 26B withone-to-one mapping from specific internal ports 22A, 22B and certainother VLANs (e.g., 110, 210) are associated with another external port26C with one-to-one mapping from a specific internal port 22C. Loss of aspecific external link does not interrupt the internal path between agiven host computer and the chassis management subsystem. Internal andexternal ports are assumed to follow an Ethernet protocol for thisillustration. An alternate communications path between the hostsubsystems and the chassis management subsystem is optional.

Although the operation of each host computer 12A-C will generally be thesame, the operation of the host computer 12A will be described indetail. The host computer 12A actively polls or queries the designatedintermediate Layer 2 device 20A to determine whether the external linkis active. In this case, the device 20A maintains a port status recordindicating the current status of each external port of the device 20A.Specifically, a local agent 15A of the host computer 12A is preferablyused to send the query to an L2 agent 21A of the designated intermediateLayer 2 device 20A. Alternatively, the port status record may bemaintained by the intermediate proxy device 40, in which case the hostcomputer 12A sends queries to the device 40. For example, the localagent 15A of the host computer 12A may send the query to a proxy agent41 of the intermediate proxy device 40 over one or the availableinternal communication paths (using path 32 through the switch or usingthe direct path 36). With respect to the functions of the presentinvention, the proxy agent 41 would operate in the same manner as the L2agent 21A, except for the apparent differences in the path of trafficwith the host computers.

The Layer 2 switch 20A reads a packet header in each communication sentby the host computer and distinguishes between traffic types (via a4-byte field in packet header that includes the VLAN value). Thisinformation allows the switch 20A to pass data traffic from a hostcomputer 12A through an external port 26A to the network 45 (and/or inthe reverse direction), while acting as a switch to send managementtraffic from the host computer 12A to the chassis management subsystem40 via a secure internal VLAN (and/or in the reverse direction).

When the local agent 15A sends a query to the agent maintaining the portstatus record (either L2 agent 21A or proxy agent 41), the particularagent response to the local agent with the status of the external portthat is associated with the local agent 15A. Optionally, the particularagent may use the source MAC address or other unique content of thequery packet to determine the physical identification of the internalport, thus forming an index into the port status table and indicatingwhich external port status is being requested.

If the response indicates to the local agent 15A that the associatedexternal port 26A is inactive, then the local agent 15A redirects datatraffic away from external port 26A of the designated switch device 20Ato the external port 28A of the alternate switch device 20B. Asmentioned previously, secure internal VLAN traffic between the hostcomputer 12A and the chassis management subsystem 40 can continuewithout being redirected, due to the fact that the internal port 22Aremains active.

Once the local agent 15A has redirected data traffic away from theexternal port 26A, the agent 15A will periodically query the agentmaintaining the port status record. If the local agent 15A receives aresponse indicating that the designated external port 26A has againbecome active (i.e., reactivated), then the local agent 15A will returnto directing data traffic of VLAN (100, 200) through the external port26A of the designated switch device 20A rather than the alternate switchdevice 20B. However, it should again be recognized that the local agent15A may balance traffic between the two switch devices 20A, 20B when theboth external ports 26A, 28A are active.

Another embodiment of the invention is implemented using a full L2switch rather than a pass-through switch. Although the method isparticularly suited to a pass-through L2 switch that will only send hosttraffic to one external port and to the internal management module, themethod may also be implemented with a general L2 switch that can passtraffic among blade servers 12A-C. In this embodiment, a networkadministrator establishes group associations that represent thecollection of internal and external ports that have a common VLAN. Morespecifically, a full L2 switch can be partitioned into multiple groups,with each internal host group having network access via a unique set ofexternal ports. However, rather than deactivating all of the internalports grouped with an external port that is lost in order to causefailover to the alternate switch, this embodiment allows the designatedinternal ports to remain active for management traffic and causes thehost stations to redirect the data traffic to the alternate internalports.

In an additional embodiment, the invention may be carried out using anL2 switch that implements trunk failover, with the internal ports beingdeactivated by the switch when associated external ports are inactive.This creates the same problem with regard to loss of secure managementVLANs between the blade and the chassis management module. Because theL2 switch firmware, such as the L2 agent, already maintains a portassociation record (i.e., an association between one or more internalports and one or more external ports), this embodiment causes the switchto deactivate only those internal ports that are associated with aunique subset of the external ports (LACP group, Etherchannel, etc.).Accordingly, a PING or ARP query from a server blade is associated withthe status of the associated group of external ports, rather than asingle external port. The L2 switch will issue an explicit response tothe PING/ARP query as a positive indication that at least one or all ofthe external ports in the group are active. Likewise, loss of allexternal ports in the group associated with the internal port willresult in the L2 switch issuing a negative response, such as noresponse, to the PING/ARP request from the server blade. However, ratherthan deactivating all of the internal ports grouped with an externalport that is lost in order to cause failover to the alternate switch,this embodiment allows the designated internal ports to remain activefor management traffic and causes the host stations to redirect the datatraffic to the alternate internal ports.

FIG. 2 is a port status table that exemplifies the port status recordthat is maintained by either the intermediate Layer 2 device 20A or theintermediate proxy device 40. The port status record 50 provides theport status (column 52) for each of the external ports (column 54) ofthe device 20A. Most preferably, the port status record 50 includes theinternal port identification (column 56) that is associated or mapped toeach of the external ports. According, each row of the table of FIG. 2lists an internal port identification, the identification of theexternal port associated with the internal port, and the status of theexternal port. When the agent maintaining the port status recordreceives a query packet, the agent reads the internal port addresswithin the query and returns a response that includes the external portstatus associated with that internal port (i.e., the status in the samerow of the table containing the internal port identification).

Although the port status table of FIG. 2 includes a listing of the VLANidentifications that are associated with the internal and externalports, this information may be maintained by the local agent within thehost computer instead of, or in addition to, the agent maintaining theport status record. In fact, a listing of VLAN identifications that areassociated with the internal and external ports is preferably maintainedby the host computer. The host computer needs to be aware of which VLANsare using the external link and which are using the internal secure pathto the management module, so that the host computer can determine whichof the VLANs need to be rerouted to the alternate path when an externalport becomes inactive.

As will be appreciated by one skilled in the art, the present inventionmay be embodied as a system, method or computer program product.Accordingly, the present invention may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer-usableprogram code embodied in the medium.

Any combination of one or more computer usable or computer readablemedium(s) may be utilized. The computer-usable or computer-readablemedium may be, for example but not limited to, an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system, apparatus,device, or propagation medium. More specific examples (a non-exhaustivelist) of the computer-readable medium would include the following: anelectrical connection having one or more wires, a portable computerdiskette, a hard disk, a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flashmemory), an optical fiber, a portable compact disc read-only memory(CD-ROM), an optical storage device, a transmission media such as thosesupporting the Internet or an intranet, or a magnetic storage device.Note that the computer-usable or computer-readable medium could even bepaper or another suitable medium upon which the program is printed, asthe program can be electronically captured, via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted, orotherwise processed in a suitable manner, if necessary, and then storedin a computer memory. In the context of this document, a computer-usableor computer-readable medium may be any medium that can contain, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The computer-usable medium may include a propagated data signal with thecomputer-usable program code embodied therewith, either in baseband oras part of a carrier wave. The computer usable program code may betransmitted using any appropriate medium, including but not limited towireless, wireline, optical fiber cable, RF, etc.

Computer program code for carrying out operations of the presentinvention may be written in any combination of one or more programminglanguages, including an object oriented programming language such asJava, Smalltalk, C++ or the like and conventional procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The program code may execute entirely on the user's computer,partly on the user's computer, as a stand-alone software package, partlyon the user's computer and partly on a remote computer or entirely onthe remote computer or server. In the latter scenario, the remotecomputer may be connected to the user's computer through any type ofnetwork, including a local area network (LAN) or a wide area network(WAN), or the connection may be made to an external computer (forexample, through the Internet using an Internet Service Provider).

The present invention is described below with reference to flowchartillustrations and/or block diagrams of methods, apparatus (systems) andcomputer program products according to embodiments of the invention. Itwill be understood that each block of the flowchart illustrations and/orblock diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks.

These computer program instructions may also be stored in acomputer-readable medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide processes for implementing the functions/actsspecified in the flowchart and/or block diagram block or blocks.

Referring now to FIG. 3, a flowchart of a method 60 of the presentinvention is provided. Although the method has been described above asbeing implemented in a blade system chassis, the method may also beimplemented in a rack system where the host computer, switch device(s),and/or management systems are interconnected via cables or wirelesslinks. In step 62, a first switch directs data traffic between a hostcomputer and a network through a designated external port of a firstswitch. In step 64, the first switch monitors the active/inactive statusof the designated external port carrying the data traffic from the firstswitch. In step 66, the host computer periodically sends a query to thefirst switch requesting the status of the designated external port. Inresponse to receiving the query, the first switch provides a replycommunication to the host computer including the status of thedesignated external port according to step 68. Step 72 determineswhether the reply communication indicates that the designated externalport is active or inactive. If the designated external port is indicatedas being “active,” then the method returns to step 62 so that the datatraffic between the host computer and the network is directed throughthe designated external port. However, if the designated external portis indicated as being “inactive,” then, in step 72, the host computerredirects data traffic away from the inactive designated external portto an alternate external port without deactivating the designatedinternal port. Preferably, the designated internal port continues to beused for secure internal LAN communications, such as between a hostcomputer and a management entity. After step 72, the method returns tostep 64, such that the switch monitors the status of the designatedexternal port. The periodic queries of step 66 and the responses of step68 also continue. Accordingly, the data traffic is directed to thedesignated external port whenever it is active, but is redirected to thealternate external port whenever the designated external port isinactive. Note that the host computer does not rely upon responses froman external remote computer or other member of the external network todetermine the status of the external communication link. Furthermore,communications between the host computer and the management entity maycontinue uninterrupted by an inactive external port.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,components and/or groups, but do not preclude the presence or additionof one or more other features, integers, steps, operations, elements,components, and/or groups thereof. The terms “preferably,” “preferred,”“prefer,” “optionally,” “may,” and similar terms are used to indicatethat an item, condition or step being referred to is an optional (notrequired) feature of the invention.

The corresponding structures, materials, acts, and equivalents of allmeans or steps plus function elements in the claims below are intendedto include any structure, material, or act for performing the functionin combination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but it not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A method comprising: a first switch monitoring the status of adesignated external port, wherein the status of the designated externalport is selected from the group consisting of active and inactive; ahost computer periodically sending a query to the first switch torequest the status of the designated external port, wherein the hostcomputer has a first connection to a designated internal port that ismapped to the designated external port of the first switch and a secondconnection to an alternate internal port that is mapped to an alternateexternal port; in response to receiving the query, the first switchproviding a reply communication to the host computer, wherein the replycommunication includes the status of the designated external port; andin response to receiving the reply communication from the first switchindicating that the status of the external port is inactive, the hostcomputer redirecting outbound VLAN traffic away from the inactivedesignated external port through the alternate internal port to thealternate external port without deactivating the designated internalport.
 2. The method of claim 1, further comprising: the host computercontinuing to use the designated internal port while the designatedexternal port is inactive.
 3. The method of claim 2, wherein the hostcomputer continues to the use designated internal port to carry VLANtraffic directed to external ports that remain active, VLAN traffic witha chassis management entity, or a combination thereof.
 4. The method ofclaim 2, further comprising: maintaining a port status record of thecurrent status of each external port of the first switch.
 5. The methodof claim 3, further comprising: maintaining a port association recordthat associates each external port of the first switch with an internalport of the first switch.
 6. The method of claim 5, further comprising:the first switch using a host computer identification contained in thequery to identify the internal port to associate with the external portin the port association record.
 7. The method of claim 6, wherein theport status record is maintained by the management entity, the methodfurther comprising: the first switch forwarding the query to themanagement entity; the management entity acquiring the external portstatus information from the first switch; and the management entityproviding the designated external port status to the host computer. 8.The method of claim 7, wherein the query and response are sent betweenthe host computer to the management entity via a direct communicationpath.
 9. The method of claim 6, wherein the port status record ismaintained by the first switch, the method further comprising: the firstswitch providing the external port status to the host computer.
 10. Themethod of claim 9, further comprising: after receiving a replycommunication from the first switch that the external port is inactive,the host computer periodically sending a query to the first switchrequesting the status of the external port; and in response to receivinga reply communication from the first switch that the designated externalport is active, the host computer redirecting VLAN traffic away from thealternate external port through the designated internal port to thedesignated external port.
 11. The method of claim 1, wherein the hostcomputer is one of a plurality of blade servers in a blade systemchassis.
 12. The method of claim 1, wherein each of the internal andexternal ports are Ethernet ports.
 13. The method of claim 1, whereinthe first switch provides the status of the designated external port tothe host computer by issuing a positive response when the designatedexternal port is active.
 14. The method of claim 13, wherein the firstswitch provides the status of the designated external port to the hostcomputer by issuing a negative response when the external port isinactive.
 15. The method of claim 14, wherein the negative response isno response.
 16. The method of claim 1, further comprising: the hostcomputer maintaining a record of VLAN identifications associated withthe designated external port.
 17. The method of claim 1, wherein each ofthe internal and external ports are designated host interface andnetwork interface ports, respectively, within a standalone networkswitch.
 18. The method of claim 1, wherein the alternate internal portand the alternate external port are included in the first switch. 19.The method of claim 1, wherein the alternate internal port and thealternate external port are included in a second switch that isindependent of the first switch.
 20. The method of claim 19, wherein thehost computer, the first switch, and the second switch are separatephysical units within a distributed system.